Experts: the importance of independence

In a large number of cases that litigate, expert evidence is required. Expert evidence is evidence of technical or scientific matters, provided by an independent expert witness with expertise in his or her field. It is usually used to assist the court when the lawyers (including the judge) do not have the requisite technical or specialist knowledge. This could be on any topic, from the fitting of boilers for a contract dispute to the valuation of properties for a probate dispute or even the assessment of someone's medical and care needs.

Crucially, an expert must be independent. The expert witness' primary duty is to help the court, and this duty overrides any duty which he may have to those instructing him. If, on instruction, an expert finds that he has any connection with any of the parties involved, he/she should immediately declare it and an alternative expert will usually be found.

This point of independence was recently tested in a case that went to the Court of Appeal (EXP v Barker [2017] EWCA Civ 63). A medical expert, Dr Molyneux, failed to disclose that he had trained the Defendant, a neuroradiologist, on whose behalf he was giving evidence and that they had "worked together closely for a substantial period".

The "close connection" didn't in fact emerge until an "unguarded moment" when Dr Molyneux referred to the Defendant, Dr Barker, by his middle name, 'Simon', the name by which he was only known to friends and close acquaintances.

The expert in this case was required to assess whether a competent radiologist should have identified an abnormality on a brain scan. Dr Barker had reviewed the scan and reported it to be "entirely normal".

It emerged that Dr Molyneux had in fact trained the defendant for a period of seven years. As the revelation only came during the trial, it was too late for an alternative expert to be called. Although entitled to completely exclude the expert's evidence, the trial judge instead continued but the eight given to his views was lessened so much as to amount to almost nothing.

Irwin LJ acting in the Court of Appeal said that "Our adversarial system depends heavily on the independence of expert witnesses, on the primacy of their duty to the court over any other loyalty or obligation, and on the rigour with which experts make known any associations or loyalties which might give rise to a conflict." He concluded that the trial judge had been fully entitled to take the view that, given the connection between the two men, the weight given to Dr Molyneux's views should be "considerably diminished".

This is a very unusual case as any competent and trustworthy expert is obliged to declare any interest or bias to the lawyers liaising with him before accepting any instructions, let alone ahead of any trial.